Influence of maximal vasodilatation on glucose and sodium blood-tissue transport in canine heart

Vascular conductance ( G = flow pressure ) and permeability-surface products ( PS) of sodium and glucose were measured in the control state and during continuous infusion of vasodilating drugs in the isolated spontaneously beating canine heart perfused with blood at constant flow. PS was determined by means of the first-circulation multiple tracers dilution method. Mean control G was 0.77 ml × min −1 × mm Hg −1 × 100 g. The extent of vasodilatation was assessed by the ratio G- drug G- control :papaverine, mean ratio 3.70 (2.59–4.73); dipyridamole, 3.50 (1.67–5.88); norepinephrine, 2.65 (1.18–4.23); nitroglycerin, 2.27 (1.66–3.25). The ratio for maximal vasodilatation was estimated to be 4–5. PS-Na and PS-glucose increased in a graded fashion with vasodilatation. With maximal vasodilatation the greatest increase observed in PS-Na was twofold, in PS-glucose 2.4-fold. The increase in PS most likely results from a change in capillary surface area. These data demonstrate a large reserve of capillary transport capacity and a wide range of possible control of transcapillary diffusion in the coronary microcirculation.